This invention relates to an air filter assembly, and is an improvement over U.S. Pat. No. 3,789,589 entitled "High Performance Filter Assembly" and assigned to a common assignee.
The aforementioned U.S. patent discloses a filter assembly for use with air treating systems such as furnaces and the like which included an outer casing 6 for attachment to the return air duct of a funance. An inner drawer 7 having a front and rear door was removably mounted in the casing for sliding movement therein, and mounted a filter media of the high efficiency type. A combination of stop bars 59 and lugs 60, together with a special dimensioning of the front drawer door 30 as compared to the rear drawer door 31, prevented inadvertent installation of the drawer backwards or in inverted position. Furthermore, the casing door of the prior patent was secured in place by tightening nuts 18.
In addition and in the prior patent, when the drawer was inserted into the casing and reached the end of its inward travel, suitable camming devices 62 and 63 on the drawer doors cooperated with a downstream casing flange 12 to shift the drawer in an upstream direction to effect a seal with the casing.
The casing of the prior patent was constructed with perpendicular flanges 13 and 14 disposed around its upstream and downstream openings for securement to suitable ductwork. Also, the casing cover 10 protruded outwardly beyond the casing sides.
Although the prior filter assembly has had substantial commercial success over the years, it was designed to be made of metallic material, which caused the assembly to be rather heavy and thus somewhat difficult to install and work with. It thus has recently become desirable to develop a filter assembly of the general type disclosed in the aformentioned patent, but which could incorporate numerous plastic parts and have a more advantageous construction, such as being mountable flush to the furnace, being lighter in weight, and being simplified and less costly to manufacture. The present invention is directed to providing such an improved assembly.
In accordance with the various aspects of the present invention, an air filter assembly includes an outer casing having end, rear and downstream portions which are generally planular and thus easily settable on the floor during installation, with the downstream portion being mountable flush to a furnace or the like. An inner filter-holding drawer is provided for easy insertion and removal from the open front casing portion. At least one end wall of the casing is provided with a springable latch adjacent the casing front opening and which snappingly engages and holds a cover in place when the drawer is within the casing.
The drawer may be made of plastic and its end walls include external grooves which are adapted to slide over rails correspondingly mounted internally of the casing side walls. The tolerances are such that the grooves are wider than the rails so that the drawer is easily slideable within the casing.
Protrusions are disposed on the downstream sides of the rail rear end portions and are engaged by the downstream groove edges as the drawer reaches its rearmost position, thus forcing the drawer's rear end portion downstream so that the groove's rear upstream edges move into sealing engagement with the upstream rear end portions of the rails. Likewise, a cam is disposed on the downstream groove sides of the drawer at their front end portions, the cam forcing the drawer's front end portion to move transversely on the rails in a downstream direction so that the upstream front end edge portions of the grooves seal against the rails. The downstream shifting of the drawer compliments the defect of the air pressure during operation of the unit, said air pressure tending to also force the drawer downstream, thus sealing the upstream sealing surfaces.